What do you guys think is a reasonable price for a 3.9 open diff, half-shafts, mustache bar, etc. from a pick-a-part Z?

Frank

Pick-a-parts that allow you to pull your own parts probably won't charge more than $50 for that. They can't warranty the bearing and seals. $75 tops. unless it's an LSD diff. If the seals and bearings are bad, it's basically scrap metal until you spend big bucks on the rebuild.